1. Field of the Invention
present invention relates to a personal identification system, and more particularly, to an iris recognition system for identifying persons by recognizing the iris of either eye.
2. Background of the Related Art
As the population of the world has increased and civilization has developed, personal identification has become important. In particular, in airports, financial agencies, research institutes, etc., a variety of methods for identifying persons are used for purposes of maintaining security or controlling access to premises.
The most common such method is an identification card. The identification card may assume a wide variety of forms, such as a simple card bearing a stamp, a card having a magnetic film or IC chip, etc., so as to identify a certain person. However, such an identification card has several limitations for personal identification, such as a risk of loss and a possibility of copying.
Attempts have been made to identify persons using their biological characteristics without any additional identification measures. Such schemes include fingerprint analysis, signature analysis, iris analysis, and the like. The analysis of the iris is performed without any physical contact, unlike other biological identification methods. Iris analysis is appropriate for rapid measurement, because a computer compares an iris pattern captured by a camera with a pre-stored iris pattern. Because no two irises are identical, even in the same person, precise identification is possible with this technique.
An iris recognition system in general includes a guidance unit for guiding an eye to a predetermined position in front of a lens of the iris recognition system in order to image the iris, and a lighting unit for illuminating the eye by radiating light of a predetermined luminosity. The system also includes an image recognition unit having an optical system consisting of a plurality of lenses for gathering light and a pickup device for imaging the iris.
FIG. 1 schematically illustrates an iris recognition system according to the conventional art. The iris recognition system mainly includes a front case 10 and an image recognition unit 3. At the center of the front case 10, a guidance unit 20 is disposed to guide an eye of a person to be positioned on the optical axis of the iris recognition system. In front of the image recognition unit 3, an optical system having a plurality of lens 5 is disposed. At the rear of the image recognition unit 3, a pickup device 7 for detecting an image passed through the lenses 5 is installed. Below the image recognition unit 3, a fixing frame 4 fixes the image recognition unit 3 to an enclosure 4 by a connecting unit 6.
In the thusly configured iris recognition system, an image of the eye (e) of a person is delivered to the pickup device 7 via the lens 5, and then the image of the iris of the eye is recognized. The iris image thusly detected from the pickup device 7 is compared with an image previously registered in a computer (not shown).
In order to precisely detect the iris, an image of the iris must be precisely captured in the pickup device. In order for the iris image to precisely reach the pickup device via the optical system, optical axes of the guidance unit for guiding the eye, the optical system having a plurality of lenses, and the pickup device for imaging the iris of an eye must all coincide. In other words, each center of the guidance unit, optical system, and pickup device must be in a straight line. No matter how slightly the guidance unit, optical system, and pickup device deviate from the same optical axis, it becomes impossible to precisely recognize the iris. So, it is very important to precisely adjust the optical axes of the components of the system. In an actual production process, however, optical axes of these components may not match one another. In particular, even though the optical axis of the optical system of the image recognition unit precisely matches that of the pickup device, there may occur a case that the optical axis of the guidance unit does not match that of the image recognition unit due to an assembling process.
FIGS. 2A through 2C illustrate an image 7′ captured by the pickup device 7 in several cases. In all of these three cases, the eye is disposed at the same position in front of the guidance unit. However, when the optical axis of the guidance unit is different from that of the image recognition unit, e.g., in FIGS. 2A and 2C, the iris (e′) captured in the pickup device is shown differently. FIG. 2A shows a lower part of the iris in a cut-off state, and FIG. 2C shows an upper part of the iris in a similar cut-off state. Even though a person precisely locates his or her eye in front of the guidance unit, the reliability of the iris recognition system will be reduced unless the entire image of the iris (e′) is present on the pickup device 7.
Hence, there is a need to prevent such a defective image by having some way to adjust the device when the optical axis of, e.g., the guidance unit 20 does not match the optical axes of the other components.